Host rescan for logical volume migration

ABSTRACT

During preparation for migration of a logical volume from a source data storage appliance to a destination data storage appliance, a determination is made as to whether at least one host that accesses a copy of the logical volume contained in the source data storage appliance is managed by a host administration server. In response to determining that at least one host that accesses the copy of the logical volume contained in the source data storage appliance is managed by the administration server, a rescan request is transmitted to the administration server. The rescan request causes the host administration server to instruct each host that is managed by the host administration server that accesses the copy of the logical volume contained in the source data storage appliance to perform a rescan operation to discover at least one new path to the logical volume.

TECHNICAL FIELD

The present disclosure relates generally to techniques for providing alogical volume of non-volatile data storage from a data storage systemto a host computer system, and more specifically to technology forcausing one or more hosts accessing a logical volume on a source datastorage appliance to automatically perform a rescan operation in orderto discover a path to a destination data storage appliance prior tomigrating the logical volume from the source data storage appliance tothe destination data storage appliance.

BACKGROUND

Data storage systems are arrangements of hardware and software thattypically provide non-volatile data storage from non-volatile datastorage devices that they contain or are communicably connected to, suchas magnetic disk drives, electronic flash drives, and/or optical drives.Data storage systems service host I/O operations (e.g. I/O reads,writes, etc.) that they receive from host computers (“hosts”). Thereceived host I/O operations specify one or more logical data storageobjects (e.g. logical volumes, sometimes also referred to as logicalunits or “LUNs”), and indicate host I/O data that is to be written to orread from the storage objects. Data storage systems include specializedhardware and execute specialized software that process incoming host I/Ooperations and perform various data storage tasks to organize and securethe host I/O data that is received from the hosts and store the receivedhost I/O data on the physical non-volatile data storage devices of thedata storage system. A data storage system may sometimes include orconsist of a cluster of data storage appliances.

Under various types of circumstances, it may be desirable to migrate alogical volume, e.g. from a source data storage appliance to adestination data storage appliance within a cluster of data storageappliances. Examples of such circumstances include without limitationresource imbalances that may arise between different data storageappliances, such as an inadequate amount of resources (e.g. storage,processing, and/or network resources) being available to support thelogical volume on the source data storage appliance, and a sufficient ormore sufficient amount of resources being available to support thelogical volume on the destination data storage appliance.

SUMMARY

When a logical volume is migrated from a source data storage applianceto a destination data storage appliance, a copy of the logical volumemay be created in the destination data storage appliance, and host datastored in a copy of the logical volume contained in the source datastorage appliance moved to the copy of the logical volume contained inthe destination data storage appliance. Migration of the logical volumemay cause the host or hosts that, prior to the migration, accessed thecopy of the logical volume contained in the source data storageappliance, to access the copy of the logical volume contained in thedestination data storage appliance after the migration.

The disclosed technology advantageously avoids shortcomings that mayarise with regard to performing host rescan operations prior tomigrating the logical volume, in order for the hosts to discover a pathto the copy of the logical volume contained in the destination datastorage appliance. Specifically, to prepare for migrating the logicalvolume from the source data storage appliance to the destination datastorage appliance, a path to the copy of the logical volume in thedestination data storage appliance is created, so that the path to thecopy of the logical volume in the destination data storage appliance canbe discovered by each of the hosts that before the migration access thecopy of the logical volume on the source data storage appliance. Inorder for hosts to discover the path to the copy of the logical volumein the destination data storage appliance, rescan operations (e.g. SCSIrescans) must be performed by the hosts. However, in some previoustechnologies, the rescan operations had to be manually performed on thehosts by a human administrator. The requirement of such manual rescanoperations introduced the possibility of human errors, and consumedsignificant amounts of administrator time. In the event that human errorresulted in the rescan operation not being performed for one or morehosts that access the logical volume to be migrated, or in the eventthat the rescan operation was incorrectly or only partly performed forone or more hosts, situations sometimes arose in such previoustechnologies that caused a data unavailability condition to occur withregard to the host data stored on the logical volume.

It would accordingly be desirable to have new technology that reducesthe risk of human errors or mistakes with regard to rescan operationsthat are performed in preparation for migrating a logical volume from asource data storage appliance to a destination data storage appliance.

To address the above described and/or other technical problems, thedisclosed technology operates, during preparation for migration of alogical volume from a source data storage appliance to a destinationdata storage appliance, by detecting whether at least one host thataccesses a copy of the logical volume contained in the source datastorage appliance is managed by a host administration server. Inresponse to detecting that at least one host that accesses the copy ofthe logical volume contained in the source data storage appliance ismanaged by the host administration server, a rescan request istransmitted to the host administration server. The rescan request causesthe host administration server to instruct each host that is managed bythe host administration server that accesses the copy of the logicalvolume contained in the source data storage appliance to perform arescan operation, thus enabling those hosts to discover a new path tothe logical volume on the destination data storage appliance.

In some embodiments, the disclosed technology may perform the steps ofi) detecting whether at least one host that accesses the copy of alogical volume contained in the source data storage appliance is managedby the host administration server, and ii) transmitting the rescanrequest to the host administration server, in response to receipt of arequest to migrate the logical volume from the source data storageappliance to the destination data storage appliance.

In some embodiments, prior to transmitting the host rescan request tothe host administration server, the disclosed technology may create acopy of the logical volume in the destination data storage appliance. Apath to the copy of the logical volume contained in the destination datastorage appliance is discoverable by the rescan operation performed byeach host that is managed by the host administration server.

In some embodiments, the path to the copy of the logical volumecontained in the destination storage appliance may include a target portcontained in the destination data storage appliance through which thecopy of the logical volume contained in the destination data storageappliance can be accessed.

In some embodiments, prior to migrating the logical volume, thedisclosed technology may set a path state of the path to the copy of thelogical volume contained in the destination data storage appliance tounavailable.

In some embodiments, the disclosed technology may set the path state ofthe path to the copy of the logical volume contained in the destinationdata storage appliance to unavailable at least in part by storing thepath state of the path to the copy of the logical volume contained inthe destination storage appliance within the source data storageappliance. In some embodiments, the disclosed technology may set thepath state of the path to the copy of the logical volume contained inthe destination data storage appliance to unavailable at least in partby storing the path state of the path to the copy of the logical volumecontained in the destination storage appliance within the destinationdata storage appliance.

In some embodiments, the disclosed technology may begin migration of thelogical volume from the source data storage appliance to the destinationdata storage appliance at least partly in response to detecting that allhosts that accessed the copy of the logical volume contained in thesource data storage appliance prior to migration have performed a rescanoperation.

In some embodiments, migrating the logical volume from the source datastorage appliance may include moving host data stored in the copy of thelogical volume contained in the source data storage appliance to thecopy of the logical volume contained in the destination data storageappliance.

In some embodiments, migrating the logical volume from the source datastorage appliance may include changing the path state of the path to thecopy of the logical volume contained in the destination data storageappliance from unavailable to active.

In some embodiments, migrating the logical volume from the source datastorage appliance to the destination data storage appliance may includechanging a path state of a path to the copy of the logical volumecontained in the source data storage appliance from active tounavailable.

Embodiments of the disclosed technology may provide significantadvantages over previous technologies. For example, embodiments of thedisclosed technology may advantageously reduce or eliminate the need fora human administrator to manually perform rescan operations on one ormore hosts when preparing for migration of a logical volume. Embodimentsof the disclosed technology may accordingly reduce the possibility ofhuman errors, and require less administrator time. As a result, thedisclosed technology avoids situations in which the migration of thelogical volume fails or is delayed for one or more hosts, and thereforeprevents data unavailable conditions from occurring with regard to hostdata that is stored in the logical volume being migrated.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages will beapparent from the following description of particular embodiments of thepresent disclosure, as illustrated in the accompanying drawings in whichlike reference characters refer to the same parts throughout thedifferent views. The drawings are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of variousembodiments of the present disclosure.

FIG. 1 is a block diagram showing an example of components in someembodiments in an example of an operational environment;

FIG. 2 is a block diagram showing an example of components in someembodiments while hosts perform rescans on data storage appliances;

FIG. 3 is a block diagram showing an example of components in someembodiments after hosts have performed rescans on the data storageappliances;

FIG. 4 is a block diagram showing an example of components in someembodiments after the logical volume has been migrated from the sourcedata storage appliance to the destination data storage appliance; and

FIG. 5 is a flow chart showing an example of steps performed duringoperation of some embodiments.

DETAILED DESCRIPTION

Embodiments will now be described with reference to the figures. Suchembodiments are provided only by way of example and for purposes ofillustration. The scope of the claims is not limited to the examples ofspecific embodiments shown in the figures and/or otherwise describedherein.

The individual features of the particular embodiments, examples, andimplementations described herein can be combined in any manner thatmakes technological sense. Such features are hereby combined to form allpossible combinations, permutations and/or variations except to theextent that such combinations, permutations and/or variations have beenexpressly excluded herein and/or are technically impractical. Thedescription in this document is intended to provide support for all suchcombinations, permutations and/or variations.

As described herein, during preparation for migration of a logicalvolume from a source data storage appliance to a destination datastorage appliance, the disclosed technology detects whether at least onehost that accesses a copy of the logical volume contained in the sourcedata storage appliance is managed by a host administration server. Inresponse to detecting that at least one host that accesses the copy ofthe logical volume contained in the source data storage appliance ismanaged by the host administration server, the disclosed technologytransmits a rescan request to the host administration server. The rescanrequest causes the host administration server to instruct each host thatis managed by the host administration server and that accesses the copyof the logical volume contained in the source data storage appliance toperform a rescan operation to discover at least one new path to thelogical volume, e.g. a path to a copy of the logical volume contained inthe destination data storage appliance.

FIG. 1 is a block diagram showing an example of components in anoperational environment including an example of an embodiment of thedisclosed technology. As shown in FIG. 1, a Cluster 105 includesmultiple data storage appliances, shown for purposes of illustration bySource Data Storage Appliance 100, and Destination Data StorageAppliance 150. While two data storage appliances are shown for purposesof illustration in the example of FIG. 1, Cluster 105 may includeadditional data storage appliances. Moreover, the technology disclosedherein is not limited to embodiments in which clusters are made up of aspecific number of data storage appliances, and may be embodied inclusters having various other specific numbers of data storageappliances.

Each one of the data storage appliances in Cluster 105 contains and/oris communicably coupled to one or more non-volatile data storagedevices, such as one or more magnetic disk drives, one or moreelectronic flash drives, and/or one or more optical drives. In theexample of FIG. 1, Source Data Storage Appliance 100 is shown includingStorage Devices 106, and Destination Data Storage Appliance 150 is shownincluding Storage Devices 156.

Each one of the data storage appliances in Cluster 105 also includescommunication circuitry that is operable to connect to, and transmit andreceive data signals over, one or more communication networks connectingthe data storage appliances in Cluster 105 to each other, and alsoconnecting the data storage appliances in Cluster 105 to Hosts 180. Inthe example of FIG. 1, Source Data Storage Appliance 100 is shownincluding Communication Interfaces 104, and Destination Data StorageAppliance 150 is shown including Communication Interfaces 154.Communication Interfaces 104 and Communication Interfaces 154 may eachinclude or consist of SCSI target adapters and/or network interfaceadapters or the like for converting electronic and/or optical signalsreceived over the network or networks that interconnect the data storageappliances in Cluster 105, and/or a network or networks that furtherconnect the data storage appliances in Cluster 105 to Hosts 180, intoelectronic form for use by the respective data storage appliance.

For example, communications between the data storage appliances inCluster 105 may be performed using the Small Computer System Interface(SCSI) protocol, through paths in a communication network connecting theHosts 180 and the data storage appliances. The paths may include orconsist of paths between SCSI initiator ports in each of the Hosts 180and SCSI target ports in the communication interfaces of the datastorage appliances. For example, Hosts 180 are shown including Host 1182, Host 2 184, through Host N 186. Each host in Hosts 180 may includeor consist of a hardware computer system, one or more virtual machines,and/or a hypervisor on which one or more virtual machines executes. Eachhost in Hosts 180 may include one or more SCSI host adapters, providingone or more SCSI initiator ports. The communication interfaces of eachdata storage appliance in Cluster 105 may provide SCSI target adaptershaving some number of target ports. In the example of FIG. 1, forpurposes of illustration, Source Data Storage Appliance 100 is shownincluding at least Target Port 108, and Destination Data StorageAppliance 150 is shown including at least Target Port 158.

Each one of the data storage appliances in Cluster 105 includesprocessing circuitry for executing program code. In the example of FIG.1, Source Data Storage Appliance 100 is shown including ProcessingCircuitry 102, and Destination Data Storage Appliance 150 is shownincluding Processing Circuitry 152. Processing Circuitry 102 andProcessing Circuitry 152 may each include or consist of one or morecentral processing units (CPUs) and associated electronic circuitry.

Each one of the data storage appliances in Cluster 105 also includes amemory operable to store program code and/or associated data structuresoperable when executed by the processing circuitry to cause theprocessing circuitry to perform various functions and provide variousfeatures of the disclosed technology. In the example of FIG. 1, SourceData Storage Appliance 100 is shown including Memory 114, andDestination Data Storage Appliance 150 is shown including Memory 164.Memory 114 and Memory 164 may each include or consist of volatile memory(e.g., RAM), and/or non-volatile memory, such as one or more ROMs, diskdrives, solid state drives, and the like.

The memory in each data storage appliance stores various specificprogram code that is executable by the processing circuitry of the datastorage appliance, and associated data structures used during theexecution of the program code. For purposes of illustration, programcode that is executable on data storage appliance processing circuitryto cause the processing circuitry to perform operations and functionsdescribed herein with regard to each storage appliance is shown in partby logical volume migration logic stored in the memory of each one ofthe data storage appliances. For example, Logical Volume Migration Logic124 in Source Data Storage Appliance 100 is operable when executed tocause Processing Circuitry 102 to perform operations and functionsdescribed herein, including preparation for migration and migration of alogical volume, and Logical Volume Migration Logic 174 is also operablewhen executed to cause Processing Circuitry 152 to perform operationsand functions described herein, including preparation for migration andmigration of a logical volume. In some embodiments, Logical VolumeMigration Logic 124 and/or Logical Volume Migration Logic 174 may eachinclude or consist of some number of Application Programming Interfaces(APIs) that are accessible to Control Plane Component 107.

Control Plane Component 107 may be contained in the memory of andexecuted on the processing circuitry of another data storage appliancein Cluster 105, and/or contained in the memory of and executed on theprocessing circuitry of Source Data Storage Appliance 100 and/orDestination Data Storage Appliance 150, to cause such processingcircuitry to perform the operations and functions described herein,including preparation for migration and migration of a logical volume.Host I/O Processing Logic 112 in Memory 114 is operable when executed tocause Processing Circuitry 102 to process host I/O operations receivedfrom Hosts 180, e.g. SCSI commands conveyed to Source Data StorageAppliance 100 over the Paths 190 that extend from initiator ports inHosts 180 to Target Port 108, and are directed to the copy of thelogical volume in Source Data Storage Appliance 100, i.e. Logical VolumeSource Copy 110. Host I/O Processing Logic 162 in Memory 164 is operablewhen executed to cause Processing Circuitry 152 to process host I/Ooperations received from Hosts 180, e.g. SCSI commands conveyed toDestination Data Storage Appliance 150 over paths from initiator portsin Hosts 180 to Target Port 158, and directed to the copy of the logicalvolume Destination Data Storage Appliance 150, i.e. Logical VolumeDestination Copy 160.

In the example of FIG. 1, the logical volume has not yet been migratedfrom Source Data Storage Appliance 100 to Destination Data StorageAppliance 150. Prior to migration of the logical volume, hosts, such asHosts 180, only access the logical volume on Source Data StorageAppliance 100, e.g. by accessing Logical Volume Source Copy 110. Priorto preparation for migration of the logical volume, only Paths 190 havebeen established from Hosts 180 to the Logical Volume Source Copy 110 onSource Data Storage Appliance 100 (e.g. through Target Port 108). Paths190 extend from initiator ports in Hosts 180 to Target Port 108. At thepoint in time illustrated by FIG. 1, paths have not yet been establishedbetween Hosts 180 and Destination Data Storage Appliance 150. Further inthe example illustrated by FIG. 1, Paths 190 have a state of “active”(e.g. Active-Optimized or Active-Non-Optimized), which indicates toHosts 180 that Logical Volume Source Copy 110 can be accessed over Paths190. Indications of the path state for each path in Paths 190 may bestored in Logical Volume Path State 118 and/or Logical Volume Path State168. For example, each of Logical Volume Path State 118 and LogicalVolume Path State 168 may store a copy of at least a portion of theAsymmetric Logical Unit Access (ALUA) state for the logical volume beingmigrated, thus making the ALUA state for the logical volume present inand accessible to Hosts 180 from both Source Data Storage Appliance 100and Destination Data Storage Appliance 150. As it is generally known,ALUA is an industry standard protocol described in the T10 SCSI-3specification SPC-3. Logical Volume Path State 118 and Logical VolumePath State 168 may both indicate the current state of all current paths(e.g. Paths 190 in FIG. 1, Paths 190 and 192 in FIGS. 3 and 4) foraccessing the logical volume being migrated, and may be part of the ALUAstate that is associated with that logical volume. The ALUA state forthe logical volume may be obtained by Host Computer 180 with regard toeach target port group that contains a target port through which a copyof the logical volume can be accessed. Accordingly, Logical Volume PathState 118 and Logical Volume Path State 168 may be the same in SourceData Storage Appliance 100 and Destination Data Storage Appliance 150 atany given point in time, and may be obtained by Host Computer 180 byissuing a SCSI Report Target Port Group (RTPG) command to a target portgroup that contains Target Port 108, and/or by issuing an RTPG commandto a target port group that contains Target Port 158. As describedbelow, migration of the logical volume results in the states of thepaths in Paths 190 being changed to unavailable, and the states of Paths192 (see FIG. 3 and FIG. 4) being changed from unavailable to active, sothat after the logical volume is migrated from Source Data StorageAppliance 100 to Destination Data Storage Appliance 150, hosts such asHosts 180 no longer access the logical volume through Logical VolumeSource Copy 110, and instead access the logical volume through LogicalVolume Destination Copy 160.

Although certain program code and data structures are specifically shownin FIG. 1, each data storage appliance may additionally include variousother program code and/or other software constructs that are not shownbut may be additional to those shown, and that are operable in whole orin part to perform specific functions and/or operations describedherein. Such additional program logic and other software constructs mayinclude without limitation an operating system, various applications,and/or other processes and/or data structures.

Each data storage appliance in Cluster 105 may also include mappings andallocations that store indications of units of non-volatile data storagethat are allocated from the non-volatile data storage devices in thatstorage appliance to various logical volumes and/or other data storageobjects that are provided by that storage appliance. The units ofnon-volatile data storage allocated to a logical volume may be mapped torespective portions of a logical volume, and may be used to persistentlystore host data directed to the logical volume in host I/O operations(e.g. write I/O operations) that are received from Host Computer 180. A“slice” is one example of the units of non-volatile data storage (e.g.256 megabytes or 1 gigabytes in size) that may be allocated from anon-volatile data storage device to a storage object such as a logicalvolume. Host I/O Processing Logic 112 in Source Data Storage Appliance100 may store indications of units of non-volatile data storage that areallocated from Storage Device(s) 106 to logical volumes contained inSource Data Storage Appliance 100, and/or the mappings of such units ofnon-volatile data storage to respective portions the logical volumes towhich they are allocated. Host I/O Processing Logic 162 in DestinationData Storage Appliance 150 may store indications of units ofnon-volatile data storage that are allocated from Storage Device(s) 156to logical volumes in Destination Data Storage Appliance 150, and/or themappings of such units of non-volatile data storage to respectiveportions the logical volumes to which they are allocated.

The data storage appliances in Cluster 105 provide data storage servicesthat are consumed by hosts such as Hosts 180, e.g. by one or moreapplications executing in Hosts 180. Each one of the data storageappliances in Cluster 105 may expose a set of logical volumes (alsosometimes referred to as logical units or “LUNS”) to hosts including theHosts 180. In some embodiments, the data storage services provided bythe data storage appliances in Cluster 105 include one or moreblock-based storage services that provide Hosts 180 with blocks ofnon-volatile data storage from the logical volumes. Such block-baseddata storage services may, for example, employ the Small Computer SystemInterface (SCSI) protocol, the Internet Small Computer System Interface(iSCSI) protocol, and/or Fibre Channel (FC) network technology tocommunicate between the Host Computer 180 and the data storageappliances in Cluster 105.

While in the example of FIG. 1, Hosts 180 are shown external to Cluster105, the techniques described herein are not limited to suchembodiments. Alternatively, Hosts 180 may be located in whole or in parttogether with the data storage appliances in Cluster 105, as in the caseof a hyper-converged storage array that hosts both data storage andcompute resources.

Also shown in FIG. 1 is an Administration Computer 199. AdministrationComputer 199 includes processing circuitry and memory, the memorystoring program code that executes on the processing circuitry,including a Host Administration Server 190. Host Administration Server190 manages Hosts 180. Accordingly, Host Administration Server 190 hasaccess to Hosts 180 (e.g. administrator access), and is capable of andresponsible for performing and/or causing performance of administrationoperations on Hosts 180, e.g. by way of commands issued from HostAdministration Server 190 to the Hosts 180. For example, HostAdministration Server 190 may include program logic that, when executed,issues one or more commands to each one of Hosts 180 that cause each oneof Hosts 180 to perform a SCSI rescan across the data storage appliancescontained in Cluster 105, in order to discover paths to logical volumeshosted by the data storage appliances in Cluster 105. AdministrationComputer 199 is communicably connected both to Hosts 180 and Cluster105, e.g. over one or more computer networks. In some embodiments,Control Plane Component 107 operates as a client with regard to HostAdministration Server 190, and may determine information regarding Hosts180 and/or communicate various requests to Host Administration Server190 through some number of Application Programming Interfaces (APIs) inHost Administration Server 190, shown in FIG. 1 by APIs 195. In someembodiments, Control Plane Component 107 may have stored within itidentifying information that can be used to identify and communicatewith Host Administration Server 190, and credentials that may bepresented to Host Administration Server 190 to allow Control PlaneComponent 107 to gain access to the administration features provided byHost Administration Server 190, e.g. through one or more of the APIs195. For example, such identifying information for Host AdministrationServer 190 stored in Control Plane Component 107 may include an InternetProtocol (IP) address of Host Administration Server 190 and/or a FullyQualified Domain Name (FQDM) of Host Administration Server 190. Suchcredentials that allow access to Host Administration Server 190 may, forexample, include a username and password or the like that enable ControlPlane Component 107 to access a system administrator account in HostAdministration Server 190.

During operation of the components shown in FIG. 1, Control PlaneComponent 107 receives a request to migrate a logical volume, e.g.Migration Request 197. Migration Request 197 requests that Control PlaneComponent 107 perform operations that cause the logical volume to bemigrated from Source Data Storage Appliance 100 to Destination DataStorage Appliance 150, e.g. that cause host access to the logical volumeto be changed from the Logical Volume Source Copy 110 in Source DataStorage Appliance 100 to the Logical Volume Destination Copy 160 inDestination Data Storage Appliance 150. Migration Request 197 may begenerated in response to various conditions or circumstances, includingwithout limitation resource imbalances that may arise between SourceData Storage Appliance 100 and Destination Data Storage Appliance 150,such as an inadequate amount of resources (e.g. storage, processing,and/or network resources) being available to support the logical volumeon Source Data Storage Appliance 100, and/or a sufficient or moresufficient amount of resources being available to support the logicalvolume on Destination Data Storage Appliance 150, and/or otherconditions or circumstances. In some embodiments, Migration Request 197may be manually generated by a storage resource administrator user basedon automatically detected and/or manually observed resource imbalances,and passed to Control Plane Component 107 from a storage resourceadministration computer (not shown). Alternatively, Migration Request197 may be automatically generated by a Resource Balancer 196 componentthat may execute on one or more of the data storage appliances inCluster 105, and which may automatically generate Migration Request 197in response to automatic detection of one or more significant resourceimbalances within Cluster 105, e.g. between Source Data StorageAppliance 100 and Destination Data Storage Appliance 150.

In response to Migration Request 197, Control Plane Component 107performs a number of operations in preparation for the migration of thelogical volume from Source Data Storage Appliance 100 to DestinationData Storage Appliance 150. The operations performed by Control PlaneComponent 107 in preparation for migration of the logical volume fromSource Data Storage Appliance 100 to Destination Data Storage Appliance150, and performed in response to receipt of Migration Request 197,include detecting whether at least one host that accesses the logicalvolume in Source Data Storage Appliance 100 (e.g. that accesses LogicalVolume Source Copy 110 in Source Data Storage Appliance 100 prior tomigration of the logical volume), is managed by Host AdministrationServer 190. For example, the various hosts that access Logical VolumeSource Copy 110 may in some circumstances include only hosts that aremanaged by Host Administration Server 190. In other circumstances thevarious hosts that access Logical Volume Source Copy 110 may includesome hosts that are Managed by Host Administration Server 190 and someother hosts that are not managed by Host Administration Server 190, andin other circumstances the various hosts that access Logical VolumeSource Copy 110 may include no hosts that are managed by HostAdministration Server 190.

In some embodiments, Control Plane Component 107 may maintain a HostAdministration Database 198. Host Administration Database 198 may storeinformation including indications of which hosts access Logical VolumeSource Copy 110 in Source Data Storage Appliance 100, and which hostsare managed by Host Administration Server 190. The information stored inHost Administration Database 198 may be manually entered by a storageadministrator, and/or automatically obtained prior to the migration ofthe logical volume by Control Plane Component 107 from HostAdministration Server 190, e.g. through one or more of the APIs 195. Insome embodiments, Control Plane Component 107 may detect whether atleast one host that accesses the copy of the logical volume in SourceData Storage Appliance 100 prior to the migration (i.e. that accessesLogical Volume Source Copy 110 prior to the migration) is managed byHost Administration Server 190 by querying the contents of HostAdministration Database 198.

Further in response to receipt of Migration Request 197, and in responseto detecting that at least one host that accesses the logical volume onSource Data Storage Appliance 100 prior to the migration (e.g. thataccesses Logical Volume Source Copy 110 prior to the migration) ismanaged by Host Administration Server 190, Control Plane Component 107transmits Rescan Request 192 to the Host Administration Server 190. Forexample, Control Plane Component 107 may use the identificationinformation and credentials it stores regarding Host AdministrationServer 190 to gain access to Host Administration Server 190 and issueRescan Request 192 to one of the APIs 195.

Rescan Request 192 causes Host Administration Server 190 to instructeach host that is managed by Host Administration Server 190 thataccesses Logical Volume Source Copy 110 prior to the migration toperform a SCSI rescan operation with regard to the data storageappliances contained in Cluster 105 (see FIG. 2). For example, HostAdministration Server 190 may transmit Rescan Commands 194 to hostswithin Hosts 180 that access Logical Volume Source Copy 110 prior to themigration, in order to cause each one of those hosts perform a SCSIrescan operation with regard to the data storage appliances in Cluster105, so that those hosts will each discover a new path to the logicalvolume, e.g. will discover a path through Target Port 158 to LogicalVolume Destination Copy 160 in Destination Data Storage Appliance 150.In some cases, for example, all hosts that access Logical Volume SourceCopy 110 prior to the migration may be within Hosts 180, and HostAdministration Server 190 may accordingly be able to transmit RescanCommands 194 to every host that accesses the logical volume in SourceData Storage Appliance 100 prior to the migration. In cases where someof the hosts that access the logical volume on Source Data StorageAppliance 100 prior to the migration are not managed by HostAdministration Server 190, Control Plane Component 107 may additionallyor alternatively issue one or more indications (notification, alerts,etc.) to a storage resource administration computer that SCSI rescanoperations are to be manually performed on those hosts by a storageadministrator user.

In some embodiments, prior to transmission of Host Rescan Request 192 toHost Administration Server 190, and further in response to MigrationRequest 197, Control Plane Component 107, and/or Logical VolumeMigration Logic 124, and/or Logical Volume Migration Logic 174 maycreate the copy of the logical volume in the destination data storageappliance, e.g. may create Logical Volume Destination Copy 160. A pathto Logical Volume Destination Copy 160 is then discoverable by anysubsequently performed SCSI rescan operation, e.g. by each SCSI rescanperformed by a host in Hosts 180 in response to Rescan Commands 194.

In some embodiments, the path to Logical Volume Destination Copy 160 mayinclude a target port contained in Destination Data Storage System 150,e.g. Target Port 158. Logical Volume Destination Copy 160 is reachablethrough Target Port 158. Accordingly, when Logical Volume DestinationCopy 160 is created in Destination Data Storage Appliance 150, it may becreated such that it is discoverable and/or accessible through TargetPort 158, and such that paths to Logical Volume Destination Copy 160 inDestination Data Storage Appliance 150 include and/or pass throughTarget Port 158.

In some embodiments, also prior to migration and/or prior totransmission of Host Rescan Request 192 to Host Administration Server190, Control Plane Component 107, and/or Logical Volume Migration Logic124, and/or Logical Volume Migration Logic 174 may set a path state ofpaths to Logical Volume Destination Copy 160 through Target Port 158 tounavailable. For example, the ALUA state of any path to Logical VolumeDestination Copy 160 through Target Port 158 may be set to unavailableprior to migration (see Paths 192 within an unavailable state prior tomigration in FIG. 3). In this way, at the time when each path to LogicalVolume Destination Copy 160 is discovered through the SCSI rescansperformed as a result of Rescan Commands 194, no hosts in Hosts 180 willbe able to access Logical Volume Destination Copy 160 until the state ofthe path to Logical Volume Destination Copy 160 is later changed toactive as a result the logical volume being migrated from Source DataStorage Appliance 100 to Destination Data Storage Appliance 150 (seePaths 192 with an active state after migration as shown in FIG. 4).

In some embodiments, also prior to migration and/or transmission of HostRescan Request 192 to Host Administration Server 190, Control PlaneComponent 107, and/or Logical Volume Migration Logic 124, and/or LogicalVolume Migration Logic 174 may store the unavailable path state forpaths to Logical Volume Destination Copy 160 through Target Port 158within Source Data Storage Appliance 100, e.g. within Logical VolumePath State 118. Accordingly, any host that discovers a path to LogicalVolume Destination Copy 160 during a subsequently performed SCSI rescanresulting from Rescan Commands 194 also obtains the pre-migrationunavailable path state for that path from Source Data Storage Appliance100, e.g. over Paths 190.

In some embodiments, also prior to transmission of Host Rescan Request192 to Host Administration Server 190, Control Plane Component 107,and/or Logical Volume Migration Logic 124, and/or Logical VolumeMigration Logic 174 may store the unavailable path state for paths toLogical Volume Destination Copy 160 through Target Port 158 withinDestination Data Storage Appliance 150, e.g. within Logical Volume PathState 168. Accordingly, any host that discovers a path to Logical VolumeDestination Copy 160 during a subsequently performed SCSI rescanresulting from Rescan Commands 194 may also obtain the pre-migrationunavailable path state for that path from Destination Data StorageAppliance 150.

In some embodiments, Control Plane Component 107, and/or Logical VolumeMigration Logic 124, and/or Logical Volume Migration Logic 174 may beginmigration of the logical volume from Source Data Storage Appliance 100to Destination Data Storage Appliance 150 in response to detecting thatall hosts that accessed the logical volume in Source Data StorageAppliance 100 have successfully performed a SCSI rescan to discover apath to Logical Volume Destination Copy 160. Accordingly, migration ofthe logical volume may be started at least partly in response todetecting that the hosts that are managed by Host Administration Server190 and that access the logical volume in Source Data Storage Appliance100 (i.e. access Logical Volume Source Copy 110) prior to migration ofthe logical volume have performed a rescan operation. For example,Control Plane 107 may check an API within APIs 195 for a completionstatus regarding the Rescan Request 192. The completion status providedby the API may indicate whether all hosts that access the logical volumein Source Data Storage Appliance 100 prior to the migration, and thatare managed by Host Administration Server 190, have successfullyperformed a SCSI rescan of the data storage appliances in Cluster 105.In the case where all hosts that access the logical volume are withinHosts 180, and the completion status indicates that all such hosts haveperformed a SCSI rescan, then Control Plane Component 107, and/orLogical Volume Migration Logic 124, and/or Logical Volume MigrationLogic 174, may begin migrating the logical volume from Source DataStorage Appliance 100 to Destination Data Storage Appliance 150. In thecase where the completion status indicates that less than all such hostshave performed a SCSI rescan, then Control Plane Component 107 may issueone or more indications to a storage resource administration computerindicating that SCSI rescan operations must still be manually performedon the hosts on which SCSI rescans were not successfully performed as aresult of Rescan Commands 194.

Migrating the logical volume from Source Data Storage Appliance 100 toDestination Data Storage Appliance 150 may include Control PlaneComponent 107, and/or Logical Volume Migration Logic 124, and/or LogicalVolume Migration Logic 174 moving (e.g. copying) the host data stored inLogical Volume Source Copy 110 to Logical Volume Destination Copy 160.For example, moving the host data from Logical Volume Source Copy 110 toLogical Volume Destination Copy 160 during the migration process mayinclude copying one or more snapshots (point in time copies) of theLogical Volume Source Copy 110 to Destination Data Storage Appliance 150for storage into the Logical Volume Destination Copy 160, and/orsynchronously mirroring host I/O operations that are directed to thelogical volume to both Source Data Storage Appliance 100 and DestinationData Storage Appliance 150 for some period of time, such that the hostI/O operations directed to the logical volume are synchronouslyperformed on both Source Data Storage Appliance 100 and DestinationStorage Appliance 150, until the contents of Logical Volume DestinationCopy 160 are the same as the contents of Logical Volume Source Copy 110.Such host data movement between Source Data Storage Appliance 100 andDestination Data Storage Appliance 150 may be performed automatically inthe background, e.g. through one or more communication paths external toany paths between Cluster 105 and the Hosts 180, so that the datamovement is performed transparently with regard to Hosts 180, and suchthat there is no interference with or interruption to the data storageservices provided from the data storage appliances in Cluster 105 toHosts 180.

In some embodiments, migrating the logical volume from Source DataStorage Appliance 100 to Destination Data Storage Appliance 150 byControl Plane Component 107, and/or Logical Volume Migration Logic 124,and/or Logical Volume Migration Logic 174 may include changing the pathstate of the paths from one or more of the Hosts 180 to the copy of thelogical volume contained in Destination Data Storage Appliance 150 (e.g.the path state of all paths to Logical Volume Destination Copy 160 frominitiator ports in Hosts 180 through Target Port 158) from theunavailable path state to the active path state (see Paths 192 aftermigration in FIG. 4). For example, the ALUA path state for all pathsfrom initiator ports in Hosts 180 to Logical Volume Destination Copy 160through Target Port 158 may be changed from the unavailable path stateto the active path state in Logical Volume Path State 118 and/or LogicalVolume Path State 168 during the migration process.

In some embodiments, migrating the logical volume from Source DataStorage Appliance 100 to Destination Data Storage Appliance 150 byControl Plane Component 107, and/or Logical Volume Migration Logic 124,and/or Logical Volume Migration Logic 174 may include changing the pathstate of the paths from Hosts 180 to the copy of the logical volumecontained in Source Data Storage Appliance 100 (e.g. the path state ofall paths to Logical Volume Source Copy 110 from initiator ports inHosts 180 through Target Port 108) from the active path state to theunavailable path state (see Paths 190 after the migration process asillustrated in FIG. 4). For example, the ALUA path state for all pathsbetween initiator ports in Hosts 180 to Logical Volume Source Copy 110through Target Port 108 may be changed from the active path state to theunavailable path state in Logical Volume Path State 118 and/or LogicalVolume Path State 168 during the migration process.

FIG. 2 is a block diagram showing an example of components in someembodiments while one or more hosts perform rescans on data storageappliances in the Cluster 105. Specifically, one or more of the Hosts180 are shown performing SCSI Rescans 200 on the data storage appliancesin Cluster 105, e.g. in response to Rescan Commands 194 issued from HostAdministration Server 190, as shown in FIG. 1. The SCSI Rescans 200result in those hosts in Hosts 180 that accessed the logical volume inSource Data Storage Appliance 100 prior to migration of the logicalvolume (e.g. that accessed Logical Volume Source Copy 110 prior tomigration of the logical volume) discovering a path to the logicalvolume in Destination Data Storage Appliance 150 (e.g. discovering apath to Logical Volume Destination Copy 160 through Target Port 158).

FIG. 3 is a block diagram showing an example of components in someembodiments after one or more hosts in Hosts 180 have performed SCSIrescans on the data storage appliances in Cluster 105. As shown in FIG.3, after the SCSI Rescans 200 shown in FIG. 2 are performed, one or moreof the hosts in Hosts 180 have discovered Paths 192 through Target Port158 to Logical Volume Destination Copy 160. FIG. 3 shows the Paths 190and Paths 192 having path states prior to migration of the logicalvolume from Source Data Storage Appliance 100 to Destination DataStorage Appliance 150, i.e. Paths 190 have a path state of active, andPaths 192 have a path state of unavailable. Accordingly, in FIG. 3 hostsin Hosts 180 access the logical volume in Source Data Storage Appliance100, e.g. through Target Port 108.

FIG. 4 is a block diagram showing an example of components in someembodiments after the logical volume has been migrated from Source DataStorage Appliance 100 to Destination Data Storage Appliance 150. Asshown in FIG. 4, after the migration process has been completed, thepath states of Paths 190 and Paths 192 have been switched. Accordingly,after the migration process is complete, the path state of Paths 190 hasbeen changed to unavailable, and the path state of Paths 192 has beenchanged to active. Accordingly, in response to the path states shown inFIG. 4 (as may be stored in Logical Volume Path State 118 and/or LogicalVolume Path State 168), hosts in Hosts 180 that accessed the logicalvolume in Source Data Storage Appliance 100 (e.g. by accessing LogicalVolume Source Copy 110) prior to the migration process access thelogical volume in Destination Storage Appliance 150 (by accessingLogical Volume Destination Copy 160) after the migration processcompletes.

FIG. 5 is a flow chart showing an example of steps performed duringoperation of some embodiments. At step 500, a request is received tomigrate a logical volume from a source data storage appliance to adestination data storage appliance. For example, at step 500 ControlPlane Component 107 receives Migration Request 197.

At step 502, a copy of the logical volume is created in the destinationdata storage appliance. For example, at step 502, Logical VolumeDestination Copy 160 is created in Destination Data Storage Appliance150. Further at step 502, the path state for paths to the copy of thelogical volume in the destination data storage appliance is set tounavailable. For example, the path state for paths to Logical VolumeDestination Copy 160 through Target Port 158 is set to unavailable inLogical Volume Path State 118 and/or Logical Volume Path State 168.

At step 504, in order to prepare for migrating the logical volume, thecluster of data storage appliances detects whether at least one hostthat is managed by a host administration server accesses the logicalvolume prior to the migration process on the source data storageappliance. For example, Control Plane Component 107 may query HostAdministration Database 198 to determine whether any of the hosts thataccess the logical volume on Source Data Storage Appliance 100 prior tothe migration process are managed by Host Administration Server 190.

At step 506, if at least one host that accesses the logical volume onthe source data storage appliance prior to the migration process ismanaged by the host administration server, then the cluster of storageappliances transmits a rescan request to the host administration server.For example, if at least one of the hosts in Hosts 180 accesses thelogical volume on Source Data Storage Appliance 100 prior to themigration process (e.g. accesses the Logical Volume Source Copy 110prior to the migration process), then Control Plane Component 107transmits Rescan Request 192 to Host Administration Server 190. RescanRequest 192 causes Host Administration Server 190 to transmit RescanCommands 194 to Hosts 180. Rescan Commands 194 cause one or more of thehosts in Hosts 180 (e.g. at least those hosts in Hosts 180 that accessedthe logical volume in Source Data Storage Appliance 100 prior to themigration process, or alternatively all of the hosts in Hosts 180) toperform a SCSI rescan operation on the data storage appliances inCluster 105, thereby allowing such hosts in Hosts 180 to discover a newpath to the logical volume (e.g. a path to Logical Volume DestinationCopy 160 through Target Port 158).

At step 508, a determination is made as to whether SCSI rescanoperations have been performed for all hosts that accessed the logicalvolume on Source Data Storage Appliance 100 prior to the migrationprocess. For example, in the use case where all hosts that accessed thelogical volume on Source Data Storage Appliance 100 prior to themigration process are within the Hosts 180, and accordingly all hoststhat accessed the logical volume on Source Data Storage Appliance 100prior to the migration process are managed by Host Administration Server190, Control Plane Component 107 may check a completion status in one ofthe APIs 195 to detect whether Rescan Request 192 resulted in SCSIrescan operations being automatically performed on those hosts withinHosts 180. In the case where one or more hosts that accessed the logicalvolume on the Source Data Storage Appliance 100 prior to the migrationprocess are not within Hosts 180, and are accordingly not managed byHost Administration Server 190, a SCSI rescan operations must bemanually be performed on those hosts. In the case where one of the APIs195 indicates that the SCSI rescan failed or could not be automaticallyperformed on one or more of the hosts in Hosts 180 that accessed thelogical volume on Source Data Storage Appliance 100 prior to themigration process, then a SCSI rescan operation must manually beperformed on those hosts as well. FIG. 3 shows an example of the pathstates after the SCSI rescan operations have been performed for allhosts that accessed the logical volume on Source Data Storage Appliance100 prior to the migration process.

At step 510, after SCSI rescan operations have been successfullyperformed on all hosts that accessed the logical volume on the SourceData Storage Appliance 100 prior to the migration process, the logicalvolume can be migrated from the Source Data Storage Appliance 100 to theDestination Data Storage Appliance 150. For example, migrating thelogical volume from Source Data Storage Appliance 100 to DestinationData Storage Appliance 150 includes moving the host data storage inLogical Volume Source Copy 110 to Logical Volume Destination Copy 160,setting the path state each path in Paths 190 to unavailable, andsetting the path state for each path in Paths 192 active. After themigration process completes, in response to the new paths states (seeFIG. 4), hosts are able to access the logical volume in the DestinationData Storage Appliance 150 by accessing Logical Volume Destination Copy160 through Target Port 158 over Paths 192, and access to the logicalvolume on Source Data Storage Appliance 100 is discontinued.

While the above description provides examples of embodiments usingvarious specific terms to indicate specific systems, devices, and/orcomponents, such terms are illustrative only, and are used only forpurposes of convenience and concise explanation. The disclosed system isnot limited to embodiments including or involving systems, devicesand/or components identified by the terms used above.

As will be appreciated by one skilled in the art, aspects of thetechnologies disclosed herein may be embodied as a system, method orcomputer program product. Accordingly, each specific aspect of thepresent disclosure may be embodied using hardware, software (includingfirmware, resident software, micro-code, etc.) or a combination ofsoftware and hardware. Furthermore, aspects of the technologiesdisclosed herein may take the form of a computer program productembodied in one or more non-transitory computer readable storagemedium(s) having computer readable program code stored thereon forcausing a processor and/or computer system to carry out those aspects ofthe present disclosure.

Any combination of one or more computer readable storage medium(s) maybe utilized. The computer readable storage medium may be, for example,but not limited to, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a portable compact disc read-only memory (CD-ROM), anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. In the context of this document, acomputer readable storage medium may be any non-transitory tangiblemedium that can contain, or store a program for use by or in connectionwith an instruction execution system, apparatus, or device.

The figures include block diagram and flowchart illustrations ofmethods, apparatus(s) and computer program products according to one ormore embodiments of the invention. It will be understood that each blockin such figures, and combinations of these blocks, can be implemented bycomputer program instructions. These computer program instructions maybe executed on processing circuitry to form specialized hardware. Thesecomputer program instructions may further be loaded onto a computer orother programmable data processing apparatus to produce a machine, suchthat the instructions which execute on the computer or otherprogrammable data processing apparatus create means for implementing thefunctions specified in the block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function specified in the block orblocks. The computer program instructions may also be loaded onto acomputer or other programmable data processing apparatus to cause aseries of operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functionsspecified in the block or blocks.

Those skilled in the art should also readily appreciate that programsdefining the functions of the present invention can be delivered to acomputer in many forms; including, but not limited to: (a) informationpermanently stored on non-writable storage media (e.g. read only memorydevices within a computer such as ROM or CD-ROM disks readable by acomputer I/O attachment); or (b) information alterably stored onwritable storage media (e.g. floppy disks and hard drives).

While the invention is described through the above exemplaryembodiments, it will be understood by those of ordinary skill in the artthat modification to and variation of the illustrated embodiments may bemade without departing from the inventive concepts herein disclosed.

What is claimed is:
 1. A method comprising: during preparation formigrating a logical volume from a source data storage appliance to adestination data storage appliance, detecting whether at least one hostthat accesses a copy of the logical volume contained in the source datastorage appliance is managed by a host administration server; and inresponse to detecting that at least one host that accesses the copy ofthe logical volume contained in the source data storage appliance ismanaged by the host administration server, transmitting a rescan requestto the host administration server that causes the host administrationserver to instruct each host that is managed by the host administrationserver and accesses the copy of the logical volume contained in thesource data storage appliance to perform a rescan operation to discoverat least one new path to the logical volume.
 2. The method of claim 1,wherein detecting whether at least one host that accesses a copy of thelogical volume contained in the source data storage appliance is managedby the host administration server, and transmitting the rescan requestto the host administration server, are performed in response toreceiving a request to migrate the logical volume from the source datastorage appliance to the destination data storage appliance.
 3. Themethod of claim 2, further comprising: prior to transmitting the hostrescan request to the host administration server, creating a copy of thelogical volume that is contained in the destination data storageappliance, wherein a path to the copy of the logical volume contained inthe destination data storage appliance is discoverable by the rescanoperation performed by each host that is managed by the hostadministration server and accesses the copy of the logical volumecontained in the source data storage appliance.
 4. The method of claim3, further comprising: wherein the path to the copy of the logicalvolume contained in the destination storage appliance includes a targetport contained in the destination data storage appliance through whichthe copy of the logical volume contained in the destination data storageappliance can be accessed.
 5. The method of claim 4, further comprising:setting a path state of the path to the copy of the logical volumecontained in the destination data storage appliance to unavailable. 6.The method of claim 5, further comprising wherein setting the path stateof the path to the copy of the logical volume contained in thedestination data storage appliance to unavailable includes storing thepath state of the path to the copy of the logical volume contained inthe destination storage appliance in the source data storage appliance.7. The method of claim 6, further comprising: wherein setting the pathstate of the path to the copy of the logical volume contained in thedestination data storage appliance to unavailable includes storing thepath state of the path to the copy of the logical volume contained inthe destination storage appliance in the destination data storageappliance.
 8. The method of claim 7, further comprising: migrating thelogical volume from the source data storage appliance to the destinationdata storage appliance in response to detecting that each host thataccessed the copy of the logical volume contained in the source datastorage appliance prior to migration of the logical volume has performeda rescan operation.
 9. The method of claim 8, wherein migrating thelogical volume from the source data storage appliance includes movinghost data stored in the copy of the logical volume contained in thesource data storage appliance to the copy of the logical volumecontained in the destination data storage appliance.
 10. The method ofclaim 9, wherein migrating the logical volume from the source datastorage appliance includes changing the path state of the path to thecopy of the logical volume contained in the destination data storageappliance from unavailable to active.
 11. The method of claim 10,wherein migrating the logical volume from the source data storageappliance to the destination data storage appliance includes changing apath state of a path to the copy of the logical volume contained in thesource data storage appliance from active to unavailable.
 12. A systemcomprising: processing circuitry; and memory having program code storedthereon that is executable on the processing circuitry, wherein theprogram code, when executed on the processing circuitry, causes theprocessing circuitry to: during preparation for migrating a logicalvolume from a source data storage appliance to a destination datastorage appliance, detect whether at least one host that accesses a copyof the logical volume contained in the source data storage appliance ismanaged by a host administration server, and in response to detectingthat at least one host that accesses the copy of the logical volumecontained in the source data storage appliance is managed by the hostadministration server, transmit a rescan request to the hostadministration server that causes the host administration server toinstruct each host that is managed by the host administration server andaccesses the copy of the logical volume contained in the source datastorage appliance to perform a rescan operation to discover at least onenew path to the logical volume.
 13. The system of claim 12, wherein theprogram code, when executed on the processing circuitry, further causesthe processing circuitry to detect whether at least one host thataccesses a copy of the logical volume contained in the source datastorage appliance is managed by the host administration server, andtransmit the rescan request to the host administration server, inresponse to receipt of a request to migrate the logical volume from thesource data storage appliance to the destination data storage appliance.14. The system of claim 13, wherein the program code, when executed onthe processing circuitry, further causes the processing circuitry to:prior to transmitting the host rescan request to the host administrationserver, create a copy of the logical volume that is contained in thedestination data storage appliance, wherein a path to the copy of thelogical volume contained in the destination data storage appliance isdiscoverable by the rescan operation performed by each host that ismanaged by the host administration server and accesses the copy of thelogical volume contained in the source data storage appliance.
 15. Thesystem of claim 14, further comprising: wherein the path to the copy ofthe logical volume contained in the destination storage applianceincludes a target port contained in the destination data storageappliance through which the copy of the logical volume contained in thedestination data storage appliance can be accessed.
 16. The system ofclaim 15, wherein the program code, when executed on the processingcircuitry, further causes the processing circuitry to: set a path stateof the path to the copy of the logical volume contained in thedestination data storage appliance to unavailable.
 17. The system ofclaim 16, wherein the program code, when executed by the processingcircuitry, further causes the processing circuitry to: set the pathstate of the path to the copy of the logical volume contained in thedestination data storage appliance to unavailable at least in part bystoring the path state of the path to the copy of the logical volumecontained in the destination storage appliance in the source datastorage appliance.
 18. The system of claim 17, wherein the program code,when executed by the processing circuitry, further causes the processingcircuitry to: set the path state of the path to the copy of the logicalvolume contained in the destination data storage appliance tounavailable at least in part by storing the path state of the path tothe copy of the logical volume contained in the destination storageappliance in the destination data storage appliance.
 19. The system ofclaim 18, wherein the program code, when executed by the processingcircuitry, further causes the processing circuitry to: migrate thelogical volume from the source data storage appliance to the destinationdata storage appliance in response to detecting that each host thataccessed the copy of the logical volume contained in the source datastorage appliance prior to migration of the logical volume has performeda rescan operation.
 20. A non-transitory computer readable medium, thenon-transitory medium having a set of instructions stored thereon, theset of instructions, when executed on processing circuitry, causes theprocessing circuitry to perform the steps of: during preparation formigrating a logical volume from a source data storage appliance to adestination data storage appliance, detecting whether at least one hostthat accesses a copy of the logical volume contained in the source datastorage appliance is managed by a host administration server; and inresponse to detecting that at least one host that accesses the copy ofthe logical volume contained in the source data storage appliance ismanaged by the host administration server, transmitting a rescan requestto the host administration server that causes the host administrationserver to instruct each host that is managed by the host administrationserver and accesses the copy of the logical volume contained in thesource data storage appliance to perform a rescan operation to discoverat least one new path to the logical volume.